Rotary cutting tools such as end mills are used for various machining processes on workpieces. Such machining processes, generically referred to as milling operations, include the forming of slots, keyways, pockets, and the like. Several criteria must be considered with respect to the design of such tools, including the time for completing a machining operation, the amount of material removed in a cut, the quality of the cut, and the wear on the tool itself during the milling operation.
To manufacture an end-mill tool, a grinder is typically used to grind a flute face and a corresponding cutting edge on the body of the tool. The grind (grinding operation) typically starts from a position adjacent an end of the body portion, continuing to a point at or near the interface of the body portion and the shank portion, commonly referred to as an “inception location.” The grind forms a desired helical flute face and/or helical cutting edge. Prior-art end-mills typically have continuous helical flutes with continuous cutting edges helically extending from the inception location to the point (or vice-versa). The flutes function primarily for chip removal, in a manner similar to the helical flutes found on an ordinary drill bit.
It is known in the art to form flutes at a low helix angle or a high helix angle. A “low helix” (or low helical flute) is a flute that helically “winds” around a cylinder at an angle of no more than 45 degrees. A “super” low-helical flute would be a flute that winds around a cylinder at an angle of at no more than 15.degree. A “high helix” (or high helical flute) is a flute that helically winds around a cylinder at an angle of greater than 45 degrees, while a “super” high-helical flute winds around a cylinder at an angle of at least 65 degrees. Low helix angle flutes are typically employed for rough cutting while high helix angle flutes are employed for finish cutting.
Numerous variations of the grind (e.g., flute angle) have been attempted in end-mill tool design. Prior advancements relating to material removal and feed rate of end-mill cutters have been accomplished by (1) varying the spiral lead angle; (2) increasing the depth of the flutes in the body portion of the end-mill, (3) changing the radial rake; (4) changing the clearance angles of the cutting edges; and (5) forming chip splitting grooves in the flutes.
While such variations have proven successful in various applications, they are also the source of certain disadvantages and limitations. For example, such variations may weaken portions of the tool and may not be suitable for a particular applications (e.g., regarding milling time, rough cut, finish cut, etc.). Furthermore, existing end-mills are not efficient for both rough cutting and finish cutting. It is often advantageous when performing an end-mill machining operation to create many small chips, rather than fewer elongated curlicue chips. This allows, for example, rapid rate of removal of material from a workpiece without undue heating of the end-mill tool.